Manufacture of cork composition products



April 29, 1958 G. E. EHLE 2,832,097

MANUFACTURE OF coRx COMPOSITION PRODUCTS Filed Sept. 28, 1955 COMPRESS CORK PARTICLES COAT PARTICLES WITH BINDER MOLD BINDER- COATED CORK PARTICLES UNDER HEAT AND PRESSURE INVENTOR GEORGE E- EHLE ATTORNEY MANUFACTURE OF CORK COMPOSITION PRODUCTS George E. Ehle, Lancaster Township, Lancaster County, Pa, assignor to Armstrong Cork Company, Lancaster, Pa, a corporation of Pennsylvania Application September 28, 1955, Serial No. 537,267

8 Claims. (Cl. 18-48) This invention relates to the manufacture of cork composition products and is concerned particularly with the manufacture of cork tile and similar products which are made from coarsely ground cork particles bound together with a heat-converted binder.

'In the manufacture of cork tile, it is desirable to use relatively large size granules of cork to obtain an attractive appearance which cannot be successfully achieved where finely ground cork particles are used, such as are employed in the manufacture of cork gasketing compositions. Generally, virgin cork, that is the initial stripping of bark from the cork oak tree, is preferred for cork tile manufacture because of its more variegated color characteristics.

It is now known that to produce satisfactory molded cork products, it is necessary to maintain the heated mass of binder-coated cork granules in the mold under compression for a substantially longer period than is required to activate the binder. The mold dwell period is required to obtain a permanent set in the cork granules, preventing their excessive re-expansion upon release of the mass from the mold in which it is formed. If the mat is released from the mold prior to complete or substantially complete stress relaxation or permanent set of the cork granules, there is a tendency for the mat to reexpand excessively, and it may even rupture internally. A product of nonuniform density is the result in any event, and such a product is not commercially acceptable for floor tile uses.

The excessively long mold dwell period is a problem of major significance in the manufacture of cork tile utilizing a heat-convertible binder. The problem is particularly acute where virgin cork is used, for the set rate of this cork is substantially slower than the more expensive later strippings known in the art as refugo or cork wood.

It is an object of this invention to provide a method of making adhesively bound cork composition products which will require a reduced mold dwell time for stress relaxation of the cork granules.

Another object of the invention is to provide a method of treating virgin cork granules to reduce the time required for their stress relaxation.

Other objects of the invention will be clear from the following detailed description of certain embodiments of the invention.

According to this invention, the cork granules are subjected to a severe compression and working action under controlled conditions. This is preferably accomplished by passing the cork granules through the nip between a pair of rotating rolls. The rolls are set so that the granules which are passed therethrough are compressed on an average to about or less of their original volume. During passage of the granules through the rolls, the granules are subjected to an intensive rolling action and may be-tornpartially; but few, if any, of them are subdivided, and the conditions may be so controlled that subdivision is not effected in any major amount. This atom 2. would detract, in many instances, from the desired characteristics of the finished product, particularly itssurface appearance.

As an illustration of a specific embodiment of the invention, a mass of particles of virgin cork, ranging in size from /z" to 10 mesh (U. S. Standard) and having the following screen analysis, may beemployed:

TABLE I Before treatment Sieve (U. S. Standard): percent retained .371 or 5.6 .263" or 3 mesh 41.2

.185 or 4 mesh 32.0 i .131" or A5 mesh' 15.8 .093" or 8 mesh). 2.3 .065" or 10 mesh 2.0 Pan 1.1

The cork granules are at a temperature'of about F. as delivered for treatment. The granules are fed as a bank into a pair of rotating rolls, each having a smooth working surface, the rolls being l5"'in diameter, one rotating at about 15 revolutions per minute and the other at about 18 revolutions 'perminute. The spacing betweenthe rolls at the nip is in the orderof .020", and the roll temperatures are about 85 F. There will be some heat developed in the cork particles during'the treating operation.

The particles which are passed throughthe rolls are delivered therefrom in loosely agglomerated condition but are readily broken apart since nothing more than mechanical binding of the granules occurs; They are flattened out to some extent, and some of them have their surfaces torn and are ragged and irregular in shape. There is no substantial subdivision of the granules effected in this operation, however, as will be clear from the following screen analysis of a batch such as referred to above, subsequent to roll treatment:

A typical cork tile composition may be formulated asfollows:

Example Parts by weight to 10 mesh cork (U. S. Standard) Binder-19henol-formaldehyde resin 5-15 In the preparation of the composition, the following practice may be followed:

The binder is spread evenly over the treated cork particles, and the binderocated particlescare charged into a mold and compressed to a density of about 30 pounds per cubit foot. A charge of about 225 pounds may be compressed into a mat about 50X2Sx9". The mass is then heated dielectrically to a temperature of about 220 F. and is held for about 3 /2 hours in the mold. x I

This mold dwell time is:-abontuone thirdless than would be required under the same conditions utilizing the same binder but with untreated cork particles of the same size and kind. The mold dwell time will, of course, vary with the temperature of heat activation of the binder, the vapor pressure of the mass undergoing treatment, the size of the mat being made, the density to which the product is compressed, the method of heating, and other variable factors. As a general rule, however, it has been found that by the present invention the mold dwell time may be reduced by about one third, with all of the cork component being subjected to the compression and working action of the rolls. The reduction in dwell time will be lesser, of course, Where less than all of the cork particles are subjected to the treatment. The reduction when fifty percent or more of treated cork is used is generally proportional to the quantity of treated cork used; about one half the reduction indwell time being realized, for example, where one half of the cork component is subjected to the treatment under optimum conditions as later defined and the other half is untreated. The block or mat as it is called is removed from the mold after the 3 /2 hour molding period and is held under pressure until it has cooled to room temperature, about 100 F., as set forth in Gard Patent 2,601,702. The mat is then cut into sheets, and tiles are die cut therefrom and finished in the usual manner.

In the accompanying drawing, the single figure is a flow diagram, with schematically illustrated apparatus, of a method of making cork composition in accordance with the invention.

In practice of the invention, the following conditions should be followed, for best results:

Degree of compressiom-The cork granules in their passage through the nip between the rolls should be compressed on an average to about or less of their original volume. A compression as great as 99% of the original average volume may be successfully achieved if care is exercised in the feeding of the granules to the roll and if other of the conditions mentioned below are carefully observed. The improved results flowing from compresive Working of the cork granules fall off rapidly if a substantially lesser average degree of compression than 90% is effected.

Temperature conditions.-The cork at the time of delivery into the working rolls should be at a temperature below about 150 F. Improved results will be achieved if the cork granules are substantially below such temperature. The granules respond more favorably to the treatment if they are at room temperature, about 70 F. to 90 F., or even lower. Artificial cool ing of the granules may be effected, and temperatures as low as about 32 F. may be used. It will be necessary to keep the temperature of the cork above the dew point in the working area to avoid excessive accumulation of moisture in the cork, for as mentioned below, the moisture content of the cork should be carefully controlled. The roll temperatures should also be maintained below 150 F. for optimum results. The rolls may be water or refrigerant cooled. For most products, however, if the rolls are maintained at or about room temperature, in the order of 70 F. to 90 F., satisfactory results will be obtained.

Moisture content.--The presence of excessively large quantities of moisture in the cork at the time of roll working militates against proper conditioning of the cork granules. For best results, the moisture content should not exceed about 10%; and optimum results are secured when the moisture is in the order of 2% to 5%, based on the weight of the cork granules. The moisture content should not be reduced to the point Where the cork granules undergoing treatment will be subdivided because of the brittleness of the cork resulting from excessivereduction in the moisture content, Bone dry if? cork will become too brittle for successful use. The operable range is in the order of about 1% to 10%.

Particle subdivision-There should be a minimum of particle subdivision, although improved results are achieved if there is some tearing of the granules without excessive subdivision. This depends upon the nature of the final product to be produced; and, for some products, the presence of subdivided particles of smaller size than the average size of the particles delivered to the rolls is not too objectionable. For cork tile, it is preferred not to have any substantial subdivision. This can be determined readily by comparative screen analysis, as in Tables I and 11.

Roll dimensions and speeds.The length of the working rolls is not critical. Best results are achieved if the diameter of the rolls is relatively small, in the order of 12" to 15". Use of small diameter rolls provides for more intensive working of the cork granules as they enter into and pass through the nip between the working rolls. For best results, the rolls should be operated at a slight differential in speed, in the order of 1 to 1.2 to 1 to 1.5. Preferably, smooth surfaced rolls are employed, although fine grooving or other surface treatment of the rolls may aid in obtaining maximum benefit from the invention. For instance, rolls having 32 longitudinal flutes per inch have been used successfully. The rolls should, of course, be so constructed that they do not effect a major subdivision of the granules which are fed thereto. Similarly, the rolls should be operated at such relative speeds as to avoid such excessive subdivision, as previously noted. The spacing between the rolls should be in the order of .050 to .020" where cork in the order of /2 to 10 mesh is being treated. With the cork granules in the above example, ranging in size from /2 to 10 mesh, the average reduction will be in the order of to with a roll nip setting between .050" and .020. Closer spacing of the rolls may be possible, but this will depend upon the horsepower available for rotating the rolls under load, the possibility of damage to the rolls in the event of failure of the granules to be fed continuously thereto which would permit the rolls to actually come into contact with one another at certain points, depending upon the camber provided on the rolls, and other variable factors.

Cork particle size.The invention is of important significance in the treatment of cork granules, at least the major portion of which Will be held on a Ma" U. S. Standard screen, i. e. a screen, the openings of which are .131" between the wires. As noted in the screen analysis of Table I, over 90% of the granules of a typical batch of /2 to 10 mesh size cork will be within this range. As noted above, the advantages of the invention will be attained but to a lesser degree if only a portion of the cork particles are treated, and the same is true if a portion of the cork granules used are less than A" mesh in size, notwithstanding that they are so treated, for granules finer than A3 are not substantially affected by the treatment, due in part at least to the mechanical history of their preparation; finely ground cork granules have been repeatedly subjected to severe shearing and compressive forces in the process of subdivision. The improved results of the roll treatment are achieved where the granules are much larger, as defined above.

While the invention is particularly useful in the preparation of cork tile for floors and walls, it is obvious that other products may be produced utilizing the process of the present invention, such as floor underlayments, isolation blocks, and other products. The particular nature of the binder employed is not critical and forms no part of the present invention. Any of the well-known blinders may be used, and a phenolic resin binder has been used in the example merely for purposes of illustration.

I claim:

1. In a method of making cork composition, the steps comprising feeding particles of cork of A3" mesh size or larger between rotating rolls, compressing said particles in their passage through the nip between said rolls to about or less of their original volume on an average, while retaining the mass of substantially all of said individual particles undiminished through subdivision of said particles during the compressing step, forming a molded mass, the cork component of which comprises said treated cork particles, by coating the cork component with a binder and molding said binder'coated cork particles under heat and pressure.

2. In a method of making cork composition, the steps comprising feeding particles of cork of mesh size or larger and containing not more than 10% and not less than 1% of moisture between rotating rolls, compressing said particles in their passage through the nip between said rolls to about 10% or less of their original volume on an average, while retaining the mass of substantially all of said individual particles undiminished through subdivision of said particles during the compressing step, forming a molded mass, the cork component of which consists principally of said treated cork particles, by coating the cork component with a heat-convertible binder and molding said binder-coated cork particles under heat and pressure.

3. In a method of making cork composition, the steps comprising feeding particles of cork Ma" mesh size or larger and at a maximum temperature of 150 F. between rotating rolls, compressing said particles in their passage through the nip between said rolls to about 10% or less of their original volume on an average, while retaining the mass of subtantially all of said individual particles undiminished through subdivision of said particles during the compressing step, forming a molded mass, the cork component of which consists essentially of said treated cork particles, by coating the cork component with a binder and molding said binder-coated cork particles under heat and pressure.

4. In a method of making cork composition, the steps comprising feeding particles of cork of Ms" mesh size or larger and at a temperature below 150 F. between rotating rolls, the surface temperature of which is maintained at or below the temperature of said cork granules, compressing said particles in their passage through the nip between said rolls to about 10% or less of their original volume on an average, while retaining the mass of sub stantially all of said individual particles undiminished through subdivision of said particles during the compressing step, forming a molded mass, the cork component of which consists principally of said treated cork particles, by coating the cork component with a heat-convertible binder and molding said binder-coated cork particles under heat and pressure.

5. In a method of making cork composition,

the steps comprising feeding particles of cork of mesh size or larger, containing from 1% to 10% moisture, and at a temperature below 150 F. between rotating rolls, compressing said particles in their passage through the nip between said rolls to about 10% or less of their original volume on an average, partially tearing the body of some of said particles while retaining the mass of substantially all of said individual particles undiminished through subdivision of said particles during the compressing and tearing step, forming a molded mass, the cork component of which consists principally of said treated cork particles, by coating the cork component with a heat-convertible binder and molding said binder-coated cork particles under heat and pressure.

6. In a method of making cork composition, the steps comprising feeding particles of cork of Ms mesh size or larger and containing not more than 5% and not less than 2% of moisture between rotating rolls having a maximum diameter of 15", compressing said granules in their passage through the nip between said rolls to about 10% or less of their original volume on an average, while retaining the mass of substantially all of said individual particles undiminished through subdivision of said particles during the compressing step, forming a molded mass, the cork component of which comprises said treated cork particles, by coating the cork component with a binder and molding said binder-coated cork particles under heat and pressure.

7. In a method of making cork composition, comprising feeding particles of cork of A" to ten mesh size consisting essentially of cork particles of mesh size or larger between rotating rolls, the temperature of which is below 150 F., compressing said particles in their passage through the nip between said rolls to about 10% or less of their original volume on an average, partially tearing the body of some of said particles while retaining the mass of substantially all of said individual particles undiminished through subdivision of said particles during the compressing and tearing step, forming a molded mass, the cork component of which consists essentially of said treated cork particles, by coating the cork component with a binder and molding said binder-coated cork particles under heat and pressure.

8. In a method of making cork composition, the steps of claim 7 in which the cork particles and the rolls are at temperatures in the order of 32 F. to F. and the rolls are set to provide a nip opening of .020" or less and the rolls are rotated at diiferential speeds in the range between 1:12 to 1:15.

UNITED STATES PATENTS References Cited in the file of this patent the steps U. S DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent Non 2,832,097 George En Ehle April 29, 1958 It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let cers Patent should read as corrected below.

"Golumn 2, line 67, for cuhit 'reed fie "cubic column 3 y line 42, for "oomgpre'sive" reed we "e'ompreseive column 4, line '71, for "blinders read binders column 5, line 2'7, for "cork read cork of e,

Signed and sealed this 10th day of June 1958:,

(SEAL). Attest:

KARL AXLIM Attesting Officer ROBERT C WATSON Commissioner of Patents 

1. IN A METHOD OF MAKING CORK COMPOSITION, THE STEPS COMPRISING FEEDING PARTICLES OF CORK OF 1/8" MESH SIZE OR LARGER BETWEEN ROTATING ROLLS, COMPRESSING SAID PARTICLES IN THEIR PASSAGE THROUGH THE NIP BETWEEN SAID ROLLS TO ABOUT 10% OR LESS OF THEIR ORIGINAL VOLUME ON AN AVERAGE, WHILE RETAINING THE MASS OF SUBSTANTIALLY ALL OF SAID INDIVIDUAL PARTICLES UNDIMINISHED THROUGH SUBDIVISION OF SAID PARTICLES DURING THE COMPRESSING STEP, FORMING A MOLDED MASS, THE CORK COMPONENT OF WHICH COMPRISES SAID TREATED CORK PARTICLES, BY COATING THE CORK COMPONENT WITH A BINDER AND MOLDING SAID BINDER-COATED CORP PARTICLES UNDER HEAT AND PRESSURE. 